In many types of circuits it is desirable to stabilize, to detect or to synchronize a given signal to a device or to a reference signal. Several techniques have been developed to stabilize a generated signal or to detect signals in the presence of noise. As one example, a closed-loop feedback control system, such as a phase-locked loop (PLL), can be implemented to perform this function. Generally, a PLL generates and outputs a signal in relation to the frequency and phase of an input or reference signal. PLL circuitry can respond to both the frequency and the phase of the input signals, such automatically raising or lowering the frequency of an associated oscillator until the output signal is matched to the reference in both frequency and phase. PLL circuits are widely utilized in radio, telecommunications, computers and other electronic applications.
As a further example, in many communications applications, an eye pattern (also known as an eye diagram) can be generated using an oscilloscope or other display device. The eye pattern is generated based on a digital data signal from a receiver (or other source of data) that is repetitively sampled aid applied to the vertical input, while the data rate is used to trigger the horizontal sweep. The eye pattern receives is name because, for several types of coding, the pattern looks like a series of eyes between a pair of rails.